1.

The current density varies radical distance r as `J=ar^(2)`, in a cylindrical wire of radius R. The current passing through the wire between radical distance `R//3 and R//2` is,A. `(65piaR^(4))/(2592)`B. `(25piaR^(4))/(72)`C. `(65pia^(2)R^(3))/(2938)`D. None of these

Answer» Correct Answer - A
Given , `J=ar^(2)`
`i=underset(1)overset(2)intJxx2pirdr=underset(R//3)overset(R//2)intar^(2)2pirdr`
`2piaunderset(R//3)overset(R//2)intr^(3)dr=2pia|(r^(4))/(4)|_(R//3)^(R//2)`
`=(pia)/(2)[((R)/(2))^(4)-((R)/(3))^(4)]`


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